U.S. Pat. No. 5,226,123 to Vockenhuber proposes an addressing device that relies on the cable impedance to address a sequence of addressable units. That is, addressing is accomplished without using any specially coded addresses. Further all addressable units are of the same kind, and addressing is performed by a standardized signal. This innovation itself is remarkable as compared to the state prior of the art, where addressing was performed by specially coded individual addresses identifying the site of addressable units. The disclosure of the 5,226,123 patent is incorporated herein by reference.
Nevertheless, the proposed arrangement of the 5,226,123 patent has the disadvantage that high frequencies have to be used in order to address the unit, as the cable impedance is too low to sufficiently change the parameter of the standardized signal. High frequency implies a high power consumption by the used electronic components, thus making them more expensive to produce. Further, they imply high radio emissions of the used frequencies. This may make it necessary to shield the complete cable, proposed in the 5,226,123 patent in order to be compatible with the local radio emission requirements. This may have the undesirable effect of considerably raising production costs.
An additional disadvantage of the arrangement proposed in the 5,226,123 patent is the possibility of collectively addressing two nearby cells by the standardized signal. This may occur if the signal is insufficiently weakened between them. One may prevent that failure by using a higher addressing frequency, but this goes at the expense of the previously mentioned problems concerning the emitted power, the component cost, and power consumption.
Finally, one further disadvantage of an arrangement following the proposal in the 5,226,123 patent is that the impedance member, intended to weaken the standardized signal, has to be realized in the form of a capacitor, which is an electronic component that cannot be integrated on a chip.